In the well known LWG process, carbon electrode bodies, typically of cylindrical shape, are placed in end-to-end contact to form an electrically conductive column which is supported on, and also covered by, a heat insulating pack medium, e.g. carbon granules, in a furnace which provides an electrical connection at each end of the column. Electrical current, e.g. from a rectiformer, flows through the column of carbon bodies and heats the carbon bodies to graphitization temperature, e.g. 2500.degree. C.-3500.degree. C. by the Joule effect. The carbon electrode bodies, before graphitization, are formed of amorphous carbon, e.g. coke and binder, and have been previously baked at 700.degree. C. to 1000.degree. C. in accordance with conventional practices. In the course of subsequent graphitization, the amorphous carbon electrode bodies are converted to graphite at high temperatures, up to 3500.degree. C., using very large electrical currents, typically direct current (DC) in the range of 50,000 A to 150,000 A. In the LWG process, two furnaces are sometimes arranged side-by-side with the graphitizing electrical current passing up through the electrode column in one furnace then crossing over and passing back through the column in the other furnace. Apparatus for carrying out the LWG process is the subject of U.S. Pat. No. 1,029,121. Moveable apparatus for carrying out the LWG process is disclosed, for example, in U.S. Pat. Nos. 4,015,068, 4,394,766 and 4,916,714. Similar apparatus for the manufacture of silicon carbide is disclosed in U.S. Reissue Pat. No. 27,018. In a common practice of the LWG process, the time period for heating the carbon electrode to graphitization temperature (2500.degree. C.-3500.degree. C.) is typically 8-18 hours, after which electrical current is discontinued and cooling of the now graphitized electrode, and the pack material, to a safe handling temperature proceeds. The furnace pack material, which acts beneficially as a thermal insulator during the graphitization period, inhibits the rapid cooling of the graphitized electrode bodies down to a temperature at which oxidation of the graphite is substantially avoided, e.g. 900.degree. C.-1100.degree. C., and also retards the heat wave which passes from the graphite electrode through the pack material. Consequently, long cooling periods are required during which the furnace is, in effect, out of operation.